The invention relates to a frame for a sporting device for coupling to a shoe, such as a ski which is slidable or rollable by means of wheels, in particular a cross-country ski, or a skate frame for an ice-skate or roller-skate, which frame comprises:
an upper sub-frame with means for coupling to a shoe to be worn by a user; PA1 a lower sub-frame which is coupled via a pivot mechanism to said upper sub-frame for pivoting in a main plane and which is provided with or adapted to be provided with a runner or wheels; and PA1 resetting spring means for urging both sub-frames toward each other. PA1 the maximum height is about 30 mm. This maximum is determined by the space between the support tube for the runner and the shoe. PA1 the maximum length is about 150 mm. The heel support forms the criterion in this respect. PA1 the shafts forming the pivot axes may not be closer together than roughly 10 mm, since problems of strength might otherwise occur.
Such a frame is known for a skate and has been commercially available for many years under the name tumble skate.
The object of such a variable construction is to make the force exerted by the skater on the ice or the ground as great as possible so as to thereby maximize the effectiveness of muscle power and the speed to be thus achieved.
It has been found that while the known skate has the advantage of a very simple construction it is not able to realize the stated objective.
An important cause of this technical deficiency of the known skate lies in the fact that both sub-frames are connected for mutual pivoting in a zone located in the region of the tip of the shoe. While a large pivot angle can thereby be realized, the force to be exerted has an effective point of engagement located so far from the front of the foot that an effective force transfer is illusory.
The invention has for its object to embody a skate frame such that the effectiveness of the force transfer is made as great as possible, on the one hand by choosing, optionally in variable manner, the effective point of engagement of the thrust forces during skating on the basis of physiological and ergonomic considerations and on the other by allowing the user to use the calf-muscles during skating, which is not the case with known, non-variable skates and which is the case to only very small, almost negligible extent with the described known tumble skate.
What is of great importance is that the frame allows the possibility of bending the foot in a manner which is similar to that in a walking movement. This is important for a stable thrust and for the best possible effective use of the relevant muscles. The prior art skates are not capable of this.